Django Historical Records

This is from Marty Alchin's Pro Django_ book.

Setup the virtualenv

::

$ virtualenv --no-site-packages ve
$ source ve/bin/activate
(ve)$ pip install -r requirements.pip

Or install from PyPI

::

$ pip install django-historicalrecords

Import the HistoricalRecords and attach it to your model like you would a custom Django manager.

::

from django.db import models
from history.models import HistoricalRecords

class TestModel(models.Model):
    """A model for testing"""
    boolean = models.BooleanField(default=True)
    characters = models.CharField(blank=True, max_length=100)
    
    history = HistoricalRecords()

    class Admin:
        list_display = ('',)
        search_fields = ('',)

    def __unicode__(self):
        return u"TestModel"

If you run manage.py syncdb you'll see that it automatically creates a Historical version of whatever model you've attached it to.

::

(ve)$ ./manage.py syncdb
Creating table auth_permission
... // snip // ...
Creating table example_app_historicaltestmodel <- HistoricalTestModel!
Creating table example_app_testmodel
... // snip // ...

The HistoricalRecords clone the model it is attached to and adds some extra fields that allow you to track the type of change made, the timestamp of when the change was saved and it has a descriptor that will return the original object at the time of the change.

::

(ve)$ ./manage.py shell
>>> from example_app.models import TestModel
>>> tm = TestModel.objects.create(boolean=True,characters="abc")
>>> tm.history.count()
1
>>> most_recent = tm.history.most_recent()
>>> most_recent.boolean
True
>>> most_recent.characters
u'abc'
>>> tm.boolean = False
>>> tm.characters = "def"
>>> tm.save()
>>> tm.history.count()
2
>>> tm.history.all()
[<HistoricalTestModel: TestModel as of 2010-09-10 03:29:59.424761>, <HistoricalTestModel: TestModel as of 2010-09-10 03:28:31.358548>]
>>> from datetime import datetime
>>> timestamp = datetime(2010,9,10,3,28,31,358548)
>>> old_version = tm.history.as_of(timestamp)
>>> old_version.boolean
True
>>> tm.boolean
False
>>> old_version.characters
u'abc'
>>> tm.characters
'def'
>>> 

.. _Pro Django: http://prodjango.com